This research project will focus on the photodynamic damage of cell membranes and the subsequent repair of damaged membrane components. Preliminary split-dose experiments carried out with several strains of Escherichia coli suggest that acridine plus near ultraviolet light damages the cell membrane, and that cells recover from sublethal amounts of membrane damage. We propose to establish and characterize this recovery process in detail. Initial experiments will be carried out to develop a photosensitizing system that delivers maximum damage to cell membranes and minimum damage to the genome. One approach will involve the synthesis of a photodynamic polymer that is excluded from the cell interior. Additional experiments, using a variety of technique to detect lipid and protein modifications, will characterize the chemical nature of the damage. These methods, along with information obtained from split-dose experiments, will establish the conditions under which cells can recover from membrane damage. The molecular biology and biochemistry of the recovery process will be investigated with the use of metabolic inhibitors of electron transfer, RNA synthesis, protein synthesis, and lipid metabolism. And finally, mutants that are deficient in membrane repair will be isolated to aid in understanding the process.